System for depositing a film by modulated ion-induced atomic layer deposition (MII-ALD)

ABSTRACT

The present invention relates to an enhanced sequential atomic layer deposition (ALD) technique suitable for deposition of barrier layers, adhesion layers, seed layers, low dielectric constant (low-k) films, high dielectric constant (high-k) films, and other conductive, semi-conductive, and non-conductive films. This is accomplished by 1) providing a non-thermal or non-pyrolytic means of triggering the deposition reaction; 2) providing a means of depositing a purer film of higher density at lower temperatures; and, 3) providing a faster and more efficient means of modulating the deposition sequence and hence the overall process rate resulting in an improved deposition method.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Utility applicationSer. No. 10/137,851 filed May 3, 2002 which is a continuation of U.S.Utility application Ser. No. 09/812,285, filed Mar. 19, 2001. Thisapplication claims the benefit of U.S. Utility application Ser. Nos.10/137,855 and 10/137,851, both filed May 3, 2000 and also claims thebenefit of U.S. Utility application Ser. Nos. 09/812,486, 09/812,352,and 09/812,285, all filed Mar. 19, 2001. This application further claimsthe benefit of U.S. Provisional Application Nos. 60/251,795 and60/254,280, both filed Dec. 6, 2000. All of the aforementionedapplications are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of advanced thinfilm deposition methods commonly used in the semiconductor, datastorage, flat panel display, as well as allied or other industries. Moreparticularly, the present invention relates to an enhanced sequential ornon-sequential atomic layer deposition (ALD) apparatus and techniquesuitable for deposition of barrier layers, adhesion layers, seed layers,low dielectric constant (low-k) films, high dielectric constant (high-k)films, and other conductive, semi-conductive, and non-conductive thinfilms.

The disadvantages of conventional ALD are additionally discussed in acopending application with the same assignee entitled “Method andApparatus for Improved Temperature Control in Atomic Layer Deposition”,which is hereby incorporated by reference in its entirety and may befound as copending application Ser. No. 09/854,092.

2. Brief Description of the Background Art

As integrated circuit (IC) dimensions shrink and the aspect ratios ofthe resulting features increase, the ability to deposit conformal,ultra-thin films on the sides and bottoms of high aspect ratio trenchesand vias becomes increasingly important. These conformal, ultra-thinfilms are typically used as “liner” material to enhance adhesion,prevent inter-diffusion and/or chemical reaction between the underlyingdielectric and the overlying metal, and promote the deposition of asubsequent film.

In addition, decreasing device dimensions and increasing devicedensities has necessitated the transition from traditional CVD tungstenplug and aluminum interconnect technology to copper interconnecttechnology. This transition is driven by both the increasing impact ofthe RC interconnect delay on device speed and by the electromigration(i.e., the mass transport of metal due to momentum transfer betweenconducting electrons and diffusing metal atoms, thereby affectingreliability) limitations of aluminum based conductors for sub 0.25 μmdevice generations. Copper is preferred due to its lower resistivity andhigher (greater than 10 times) electromigration resistance as comparedto aluminum. A single or dual damascene copper metallization scheme isused since it eliminates the need for copper etching and reduces thenumber of integration steps required. However, the burden now shifts tothe metal deposition step(s) as the copper must fill predefined highaspect ratio trenches and/or vias in the dielectric. Electroplating hasemerged as the copper fill technique of choice due to its low depositiontemperature, high deposition rate, and potential low manufacturing cost.

Two major challenges exist for copper wiring technology: the barrier andseed layers. Copper can diffuse readily into silicon and mostdielectrics. This diffusion may lead to electrical leakage between metalwires and poor device performance. An encapsulating barrier layer isneeded to isolate the copper from the surrounding material (e.g.,dielectric or Si), thus preventing copper diffusion into and/or reactionwith the underlying material (e.g. dielectric or Si). In addition, thebarrier layer also serves as the adhesion or glue layer between thepatterned dielectric trench or via and the copper used to fill it. Thedielectric material can be a low dielectric constant, i.e. low-kmaterial (used to reduce inter- and intra-line capacitance andcross-talk) which typically suffers from poorer adhesion characteristicsand lower thermal stability than traditional oxide insulators.Consequently, this places more stringent requirements on the barriermaterial and deposition method. An inferior adhesion layer will, forexample, lead to delamination at either the barrier-to-dielectric orbarrier-to-copper interfaces during any subsequent anneal and/orchemical mechanical planarization (CMP) processing steps leading todegradation in device performance and reliability. Ideally, the barrierlayer should be thin, conformal, defect free, and of low resistivity soas to not compromise the conductance of the copper metal interconnectstructure.

In addition, electroplating fill requires a copper seed layer, whichserves to both carry the plating current and act as the nucleationlayer. The preferred seed layer should be smooth, continuous, of highpurity, and have good step coverage with low overhang. A discontinuityin the seed layer will lead to sidewall voiding, while gross overhangwill lead to pinch-off and the formation of top voids.

Both the barrier and seed layers which are critical to successfulimplementation of copper interconnects require a means of depositinghigh purity, conformal, ultra-thin films at low substrate temperatures.

Physical vapor deposition (PVD) or sputtering has been adopted as thepreferred method of choice for depositing conductor films used in ICmanufacturing. This choice has been primarily driven by the low cost,simple sputtering approach whereby relatively pure elemental or compoundmaterials can be deposited at relatively low substrate temperatures. Forexample, refractory based metals and metal compounds such as tantalum(Ta), tantalum nitride (TaN_(x)), other tantalum containing compounds,tungsten (W), tungsten nitride (WN_(x)), and other tungsten containingcompounds which are used as barrier/adhesion layers can be sputterdeposited with the substrate at or near room temperature. However, asdevice geometries have decreased, the step coverage limitations of PVDhave increasingly become an issue since it is inherently a line-of-sightprocess. This limits the total number of atoms or molecules which can bedelivered into the patterned trench or via. As a result, PVD is unableto deposit thin continuous films of adequate thickness to coat the sidesand bottoms of high aspect ratio trenches and vias. Moreover,medium/high-density plasma and ionized PVD sources developed to addressthe more aggressive device structures are still not adequate and are nowof such complexity that cost and reliability have become seriousconcerns.

Chemical vapor deposition (CVD) processes offer improved step coveragesince CVD processes can be tailored to provide conformal films.Conformality ensures the deposited films match the shape of theunderlying substrate, and the film thickness inside the feature isuniform and equivalent to the thickness outside the feature.Unfortunately, CVD requires comparatively high deposition temperatures,suffers from high impurity concentrations, which impact film integrity,and have higher cost-of-ownership due to long nucleation times and poorprecursor gas utilization efficiency. Following the tantalum containingbarrier example, CVD Ta and TaN films require substrate temperaturesranging from 500° C. to over 800° C. and suffer from impurityconcentrations (typically of carbon and oxygen) ranging from several totens of atomic % concentration. This generally leads to high filmresistivities (up to several orders of magnitude higher than PVD), andother degradation in film performance. These deposition temperatures andimpurity concentrations make CVD Ta and TaN unusable for ICmanufacturing, in particular for copper metallization and low-kintegration.

Chen et al. (“Low temperature plasma-assisted chemical vapor depositionof tantalum nitride from tantalum pentabromide for coppermetallization”, J. Vac. Sci. Technol. B 17(1), pp. 182-185 (1999); and“Low temperature plasma-promoted chemical vapor deposition of tantalumfrom tantalum pentabromide for copper metallization”, J. Vac. Sci.Technol. B 16(5), pp. 2887-2890 (1998)) have demonstrated aplasma-assisted (PACVD) or plasma-enhanced (PECVD) CVD approach usingtantalum pentabromide (TaBr₅) as the precursor gas to reduce thedeposition temperature. Ta and TaN_(x) films were deposited from 350° C.to 450° C. and contained 2.5 to 3 atomic % concentration of bromine.Although the deposition temperature has been reduced by increasedfragmentation (and hence increased reactivity) of the precursor gases inthe gas-phase via a plasma, the same fragmentation leads to thedeposition of unwanted impurities. Gas-phase fragmentation of theprecursor into both desired and undesired species inherently limits theefficacy of this approach.

Recently, atomic layer chemical vapor deposition (AL-CVD) or atomiclayer deposition (ALD) has been proposed as an alternative method to CVDfor depositing conformal, ultra-thin films at comparatively lowertemperatures. ALD is similar to CVD except that the substrate issequentially exposed to one reactant at a time. Conceptually, it is asimple process: a first reactant is introduced onto a heated substratewhereby it forms a monolayer on the surface of the substrate. Excessreactant is pumped out. Next a second reactant is introduced and reactswith the first reactant to form a monolayer of the desired film via aself-limiting surface reaction. The process is self-limiting since thedeposition reaction halts once the initially adsorbed (physi- orchemi-sorbed) monolayer of the first reactant has fully reacted with thesecond reactant. Finally, the excess second reactant is evacuated. Theabove sequence of events comprises one deposition cycle. The desiredfilm thickness is obtained by repeating the deposition cycle therequired number of times.

In practice, ALD is complicated by the painstaking selection of aprocess temperature setpoint wherein both: 1) at least one of thereactants sufficiently adsorbs to a monolayer and 2) the surfacedeposition reaction can occur with adequate growth rate and film purity.If the substrate temperature needed for the deposition reaction is toohigh, desorption or decomposition of the first adsorbed reactant occurs,thereby eliminating the layer-by-layer process. If the temperature istoo low, the deposition reaction may be incomplete (i.e., very slow),not occur at all, or lead to poor film quality (e.g., high resistivityand/or high impurity content). Since the ALD process is entirelythermal, selection of available precursors (i.e., reactants) that fitthe temperature window becomes difficult and sometimes unattainable. Dueto the above-mentioned temperature related problems, ALD has beentypically limited to the deposition of semiconductors and insulators asopposed to metals. ALD of metals has been confined to the use of metalhalide precursors. However, halides (e.g., Cl, F, Br) are corrosive andcan create reliability issues in metal interconnects.

Continuing with the TaN example, ALD of TaN films is confined to anarrow temperature window of 400° C. to 500° C., generally occurs with amaximum deposition rate of 0.2 Å/cycle, and can contain up to severalatomic percent of impurities including chlorine and oxygen. Chlorine isa corrosive, can attack copper, and lead to reliability concerns. Theabove process is unsuitable for copper metallization and low-kintegration due to the high deposition temperature, slow depositionrate, and chlorine impurity incorporation.

In conventional ALD of metal films, gaseous hydrogen (H₂) or elementalzinc (Zn) is often cited as the second reactant. These reactants arechosen since they act as a reducing agent to bring the metal atomcontained in the first reactant to the desired oxidation state in orderto deposit the end film. Gaseous, diatomic hydrogen (H₂) is aninefficient reducing agent due to its chemical stability, and elementalzinc has low volatility (e.g., it is very difficult to deliversufficient amounts of Zn vapor to the substrate) and is generallyincompatible with IC manufacturing. Unfortunately, due to thetemperature conflicts that plague the ALD method and lack of kineticallyfavorable second reactant, serious compromises in process performanceresult.

In order to address the limitations of traditional thermal or pyrolyticALD, radical enhanced atomic layer deposition (REALD, U.S. Pat. No.5,916,365) or plasma-enhanced atomic layer deposition has been proposedwhereby a downstream radio-frequency (RF) glow discharge is used todissociate the second reactant to form more reactive radical specieswhich drives the reaction at lower substrate temperatures. Using such atechnique, Ta ALD films have been deposited at 0.16 to 0.5 Å/cycle at25° C., and up to approximately 1.67 Å/cycle at 250° C. to 450° C.Although REALD results in a lower operating substrate temperature thanall the aforementioned techniques, the process still suffers fromseveral significant drawbacks. Higher temperatures must still be used togenerate appreciable deposition rates. Such temperatures are still toohigh for some films of significant interest in IC manufacturing such aspolymer-based low-k dielectrics that are stable up to temperatures ofonly 200° C. or less. REALD remains a thermal or pyrolytic processsimilar to ALD and even CVD since the substrate temperature provides therequired activation energy for the process and is therefore the primarycontrol means for driving the deposition reaction.

In addition, ta films deposited using REALD still contain chlorine aswell as oxygen impurities, and are of low density. A low density orporous film leads to a poor barrier against copper diffusion sincecopper atoms and ions have more pathways to traverse the barriermaterial. Moreover, a porous or under-dense film has lower chemicalstability and can react undesirably with overlying or underlying films,or with exposure to gases commonly used in IC manufacturing processes.

Another limitation of REALD is that the radical generation and deliveryis inefficient and undesirable. RF plasma generation of radicals used asthe second reactant such as atomic H is not as efficient as microwaveplasma due to the enhanced efficiency of microwave energy transfer toelectrons used to sustain and dissociate reactants introduced in theplasma. Furthermore, having a downstream configuration whereby theradical generating plasma is contained in a separate vessel locatedremotely from the main chamber where the substrate is situated and usinga small aperture to introduce the radicals from the remote plasma vesselto the main chamber body significantly decreases the efficiency oftransport of the second radical reactant. Both gas-phase and wallrecombination will reduce the flux of desired radicals that can reachthe substrate. In the case of atomic H, these recombination pathwayswill lead to the formation of diatomic H₂, a far less effective reducingagent. If the plasma used to generate the radicals was placed directlyover the substrate, then the deposition of unwanted impurities andparticles can occur similarly to the case of plasma-assisted CVD.

Finally, ALD (or any derivative such as REALD) is fundamentally slowsince it relies on a sequential process whereby each deposition cycle iscomprised of at least two separate reactant flow and evacuation steps,which can occur on the order of minutes with conventional valve andchamber technology. Significant improvements resulting in faster ALD areneeded to make it more suitable for commercial IC manufacturing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a deposition system suitable for modulatedion-induced atomic layer deposition (MII-ALD).

FIG. 2A depicts a timing sequence for an improved ALD methodincorporating periodic exposure of the substrate to ions.

FIG. 2B is another timing sequence for an improved ALD methodincorporating periodic exposure of the substrate to ions.

FIG. 3A shows the MII-ALD method utilizing ion flux modulation to varythe substrate exposure to ions.

FIG. 3B shows the timing of the MII-ALD method utilizing ion energymodulation to vary the substrate exposure to ions by varying thesubstrate bias.

FIGS. 4A-F show methods of modulating the MII-ALD process.

FIG. 5 shows an electrostatic chuck (ESC) system suitable for modulatingthe ion energy in the MII-ALD process: a) in topological form; and, b)as an equivalent electrical circuit.

FIG. 6 is a schematic of another embodiment of a deposition systemsuitable for modulated ion-induced atomic layer deposition (MII-ALD).

FIG. 7 is a schematic of another embodiment of a deposition systemsuitable for modulated ion-induced atomic layer deposition (MII-ALD)showing an alternative gas introduction arrangement.

FIG. 8 is a schematic of another embodiment of a deposition systemsuitable for modulated ion-induced atomic layer deposition (MII-ALD)showing an alternative gas introduction arrangement.

FIG. 9 is a schematic of another embodiment of a deposition systemsuitable for modulated ion-induced atomic layer deposition (MII-ALD)showing an alternative gas introduction arrangement.

SUMMARY AND DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to methods and apparatuses useable for thedeposition of conformal solid thin films of one or more elements at lowtemperature. More particularly, the present invention relates to anenhanced sequential or, more preferably, non-sequential atomic layerdeposition apparatus and technique suitable for deposition of barrierlayers, adhesion layers, seed layers, and low dielectric constant(low-k) films, high dielectric constant (high-k) films, and otherconductive, semi-conductive, and non-conductive thin films.

More specifically, the present invention resolves the previouslypresented problems encountered in the prior art (e.g., REALD) by 1)providing a non-thermal or non-pyrolytic means of triggering thedeposition reaction; 2) providing a means of depositing a purer film ofhigher density at lower temperatures; 3) providing a faster and moreefficient means of modulating the deposition sequence and hence theoverall process rate resulting in an improved deposition method; and, 4)providing a means of improved radical generation and delivery.

Improvements to ALD processing, e.g., the REALD mentioned previously,remain “thermal” or “pyrolytic” processes since the substratetemperature provides the required activation energy and is the primarycontrol knob for driving the deposition reaction. Alternatively, wepropose a novel approach by providing the required activation energyfrom a “non-thermal” source. In particular, we propose driving thedeposition reaction primarily via substrate exposure to impinging ionswherein the ions are used to deliver the necessary activation energy tothe near surface atoms and adsorbed reactant(s) via collision cascades.

Conventional deposition processes used in the semiconductor industry(including ALD) typically deposit materials at temperatures in the rangeof 300-600° C. The deposition method described herein can be effected atmuch lower temperatures, in practice as low as 25° C. or below. Notethat this process is ion-triggered (i.e., ion-induced) as opposed toion-assisted in that deposition will not generally occur without ionbombardment since ions are used as the primary means of providing theactivation energy required for deposition. A primary benefit ofion-induced processing is the deposition of higher density films ofsuperior purity and adhesion properties. This result occurs due to ionbombardment induced densification.

FIG. 1 illustrates a deposition system suitable for modulatedion-induced atomic layer deposition (MII-ALD). The invention describedherein also incorporates a means of modulating the exposure of thesubstrate to ions. By modulating 1) the ion flux; 2) the energy of theions striking the substrate; or a combination of (1) and (2), thedeposition reaction can be precisely toggled “on” or “off”. If the ionflux or energy is at a “low” state, then no deposition results ordeposition occurs so slowly that essentially no deposition results. Ifthe impinging ion flux or energy is at a “high” state, then depositionoccurs. Since the substrate (which may be a “bare” substrate, e.g., asilicon wafer before any films have been deposited, or it may be asubstrate which may already have had one or more films deposited on itssurface) 181 is preferably maintained at a low substrate temperature,the first and second reactants do not thermally react with anyappreciable rate or do not react at all. Instead, the depositionreaction only takes place when either the ion flux or ion energy istoggled to a suitable “high state”. The desired film thickness is builtup by repeating the ion pulses (either of flux or energy) the requirednumber of cycles. Furthermore, since modulation of the ion flux or ionenergy can occur on a much faster time scale (KHz range) than theconventional valve and pump technology used in ALD (up to minutes percycle), this deposition method is more suitable for commercial ICmanufacturing. This method shall be referred to herein as modulatedion-induced atomic layer deposition (MII-ALD).

In addition, the present invention also improves upon the prior art byemploying a microwave generated plasma 172 substantially contained inthe main chamber body 190 that is isolated via a distribution showerhead171 comprised of a series or array of apertures 175 which resolves theissues of radical generation and delivery, while preventing gas-phaseprecursor cracking (i.e., fragmentation or breaking down the precursorgas into its constituent elements) and impurity and/or particlegeneration directly above the wafer 181. The plasma is contained withinthe plasma source chamber 170 itself and is not in direct communicationwith the substrate 181. In MII-ALD, the same plasma is used to generateboth ions 177 (used to drive the surface reactions) and radicals 176(used as the second reactant), but is isolated from the first reactant100 which typically contains both the principal element(s) desired inthe end film, but also unwanted impurity containing byproducts.Therefore, primarily only the radicals 176 and ions 177 are able totravel through the showerhead apertures 175. The plasma 172 isessentially contained within the plasma source chamber and does notintermingle with the precursor gases 100, 120.

The present invention utilizes ion imparted kinetic energy transferrather than thermal energy (e.g., REALD, ALD, PECVD, CVD, etc.) to drivethe deposition reaction. Since temperature can be used as a secondarycontrol variable, with this enhancement films can be deposited usingMII-ALD at arbitrarily low substrate temperatures (generally less than350° C.). In particular, films can be deposited at or near roomtemperature (i.e., 25° C.) or below.

The system of FIG. 1 contains a substantially enclosed plasma sourcechamber 170 located in substantial communication with or, morepreferably, substantially within a main chamber body 190. The plasma 172is used to dissociate feed gases 130, 110 to generate both ions 177 andradicals 176. Typical feed gases 130 used for ion generation include,but are not restricted to Ar, Kr, Ne, and Xe. Typical feed gases 110(e.g., precursor B) used for radical generation include, but are notrestricted to H₂, O₂, N₂, NH₃, and H₂0 vapor. The ions 177 are used todeliver the energy needed to drive surface reactions between the firstadsorbed reactant and the generated radicals 176. Inductively coupled RF(e.g., 400 KHz, 2 MHz, 13.56 MHz, etc.) power 160 can be used togenerate the plasma via solenoidal coils located within or outside ofthe plasma chamber (not shown in FIG. 1). More preferably, microwave(e.g., generally 2.45 GHz or higher frequencies) power 160 is coupled tothe plasma source chamber 170 via a suitable means such as a waveguideor coaxial cable. Microwave energy can be more efficiently transferredto ionizing electrons, leading to higher ionization fractions. This isof particular importance in the generation of radicals 176 (i.e., achemical fragment of a larger molecule) such as atomic hydrogen, or anyof a number of other reactive groups such as nitrogen atoms (N), oxygenatoms (O), OH molecules, or NH molecules, or a combination thereof.These radicals serve as the second reactant. Microwave orradio-frequency (RF) power 160 is coupled to the plasma 172 via adielectric material 173, which may be a dielectric window such as quartzembedded in the chamber wall, or it may be empty space in the case of amicrowave or RF antenna located within the plasma chamber.

In addition, a distribution showerhead 171, containing a series or arrayof apertures 175 through which ions 177 and radicals 176 are deliveredto the substrate 181, isolates the main process chamber 180 from theplasma source chamber 170. A pressure drop (for example, a 5 or 10 timesdecrease in pressure, with the main processing chamber 180 being at thelower pressure) is thereby created between the plasma source chamber 170and the main processing chamber 180 to project the ions 177 and radicals176 to the substrate 181 via the distribution showerhead 171. The plasmasource chamber 170 is generally of comparable diameter to the mainchamber body 190 to enable large area exposure of the sample. The size,aspect ratio, and distribution of the showerhead apertures 175 can beoptimized to provide uniform exposure of the substrate 181 and thedesired ion 177 to radical 176 ratio. The distance between thisshowerhead 171 and the substrate 181 may vary depending on theapplication. For the processing of wafers in the IC industry, thisdistance is preferably at most two wafer diameters and more preferablyless than or equal to one half a wafer diameter.

Having a substantially enclosed plasma generation chamber 170 situatedwithin the main chamber 190 allows efficient and uniform delivery ofions 177 and radicals 176 to the substrate 181. In addition, byisolating the plasma 172 from the main chamber 180 prevents gas-phasecracking of the first reactant 100 (e.g., precursor A), which isintroduced directly to the main processing chamber 180 via a gasdistribution manifold 199. Precursor A 100 may be any one or more of aseries of gaseous compounds used for depositing semiconductors,insulators, metals or the like that are well-known in the art (e.g,PDEAT (pentakis(diethylamido)tantalum), PEMAT(pentakis(ethylmethylamido)tantalum), TaBr₅, TaCl₅, TBTDET (t-butyliminotris(diethylamino) tantalum), TiCl₄, TDMAT(tetrakis(dimethylamido)titanium), TDEAT(tetrakis(diethylamino)titanium), CuCl, Cupraselect®((Trimethylvinylsilyl)hexafluoroacetylacetonato Copper I), Cu(hfac)₂(copper (II) hexafluoroacetylacetonate), Cu(acac)₂ (copper (II)acetylacetonate), Cu(thd)₂ (copper (II)2,2,6,6-tetramethyl-3,5-heptandionate), other copper (I) and copper (II)β-diketonates, W(CO)₆, WF₆, etc.) and examples will be further discussedherein. Finally, the ion/radical distribution showerhead 171 shields thedielectric wall 173 adjacent to the supplied RF or microwave power 160against being coated by precursor A 100 during processing which candegrade power transfer to the plasma 172 in processing systems found inthe prior art. This is of particular importance in the case ofdeposition of conductors whereby if the dielectric 173 is fully exposedto the metal containing first reactant 100 (e.g., precursor A) and ifthe plasma 172 was directly generated within the main chamber 190without the use of an isolating distribution showerhead 171, then metaldeposition onto the dielectric 173 will eventually shield out RF ormicrowave power 160 from the plasma 172 such that the plasma 172 willextinguish.

FIG. 2A depicts a sequence for an improved ALD method incorporatingperiodic exposure of the substrate to ions. In this variant of themethod, ion exposure 230 begins with the introduction of the secondprecursor 220 (especially when plasma generated radicals 176 are used asthe second precursor or reactant). This figure illustrates oneembodiment of MII-ALD utilizing the apparatus described in FIG. 1. Thisresults in an enhanced sequential ALD process as follows:

1) First exposure 200: The substrate 181 is exposed to a first gaseousreactant 100 (e.g., precursor A), allowing a monolayer of the reactantto form on the surface. The substrate 181 may be at any temperaturebelow the decomposition temperature of the first gaseous reactantalthough it is preferable for the temperature to generally be less thanapproximately 350° C.

2) First reactant removal 210: The excess reactant 100 is removed.Removal can occur by evacuating 214 the chamber 180 with a vacuum pump184. The vacuum pump 184 is also capable of reducing a pressure withinthe process chamber 180 to below ambient atmospheric pressure (i.e.,subatmospheric pressure). Alternatively, removal can be achieved bypurging the chamber 180 with an inert purge gas. The inert gas purge maybe used alone or in conjunction with the evacuation 214.

3) Second exposure 220: Unlike conventional ALD, the substrate 181 issimultaneously exposed to ions 177 and a second gaseous reactant (e.g.,radicals 176) during this step with the substrate 181 (e.g., wafer)biased to a negative potential V_(bias) 185. RF power supplied to theESC electrodes 603 is used to generate ions 177 (e.g., argon-ions (Ar⁺))and radicals 176 (e.g., H atoms) and to couple the bias voltage to thesubstrate to modulate the ion energy. The ions will strike the substrate181 with an energy approximately equal to (e|V_(bias)|+e|V_(p)|) whereV_(p) is the plasma 172 potential (typically 10 V to 20 V). V_(bias)(|V_(bias)|≦150 V is desirable to prevent sputtering) is typicallychosen to be greater than V_(p) in magnitude, and is used to control theion 177 energy. A V_(bias) of −20 V to −80 V is typically sufficient todrive the deposition reaction. With the activation energy now primarilysupplied by ions 177 instead of thermal energy, the first and secondreactants react via an ion-induced surface reaction to produce a solidthin monolayer of the desired film at a reduced substrate temperaturebelow conventional ALD. The deposition reaction between the first andsecond reactants is self-limiting in that the reaction between themterminates after the initial monolayer of the first reactant 100 isconsumed.

4) Second reactant removal 210: The excess second reactant is removed byagain evacuating 216 the chamber 180 with the vacuum pump 184 and/orpurging with an inert purge gas.

5) Repeat: The desired film thickness is built up by repeating theentire process cycle (steps 1-4) many times.

Additional precursor gases (e.g., 120, 140) may be introduced andevacuated as required for a given process to create tailored films ofvarying compositions or materials. As an example, an optional exposuremay occur in the case of a compound barrier of varying composition. Forexample, a TaN_(x)/Ta film stack is of interest in copper technologysince TaN_(x) prevents fluorine attack from the underlying fluorinatedlow-k dielectrics, whereas the Ta promotes better adhesion andcrystallographic orientation for the overlying copper seed layer. TheTaN_(x) film may be deposited using a tantalum containing precursor(e.g., TaCl₅, PEMAT, PDEAT, TBTDET) as the first reactant 100 (precursorA) and a mixture of atomic hydrogen and atomic nitrogen (i.e. flowing amixture of H₂ and N₂ into the plasma source 172) as the second reactantto produce a TaN_(x) film. Simultaneous ion exposure is used to drivethe deposition reaction. Next a Ta film may be deposited in a similarfashion by using atomic hydrogen (as opposed to a mixture of atomichydrogen and nitrogen) as the second reactant. An example of a tailoredfilm stack of differing materials can be the subsequent deposition of acopper layer over the TaN_(x)/Ta bi-layer via the use of a coppercontaining organometallic e.g., Cu(TMVS)(hfac) or(Trimethylvinylsilyl)hexafluoroacetylacetonato Copper I, also known bythe trade name CupraSelect®, available from Schumacher, a unit of AirProducts and Chemicals, Inc., 1969 Palomar Oaks Way, Carlsbad, Calif.92009), Cu(hfac)₂, Cu(acac)₂, Cu(thd)₂, or other copper (I) and copper(II) β-diketonates, or inorganic precursors (e.g. CuCl) shown asprecursor C 120 in FIG. 1. The copper layer can serve as the seed layerfor subsequent electroless or electroplating deposition.

A variant of the method shown in FIG. 2A is illustrated in FIG. 2B whereion exposure is initiated after the second reactant exposure. FIG. 2Bdepicts a sequence for an improved ALD method incorporating periodicexposure of the substrate 181 to ions 177. In this variant of themethod, ion exposure 280 begins with the removal 250 of the secondprecursor 256 (especially when the second precursor or reactant is notsubjected to a plasma). Typically, this is the case where the secondprecursor or reactant is not a plasma-generated radical.

In the previous embodiments of MII-ALD, although the depositiontemperature can be lowered significantly, the first and second reactantsare still sequentially introduced into the main process chamber 180, andhence will still be a slow process; It is of particular interest toeliminate or replace the time-consuming flow-evacuation-flow-evacuationsequential nature of the process.

In the preferred embodiment of the MII-ALD process, a substrate 181heated (e.g., to a low temperature of less than or equal to 350° C.) orunheated is simultaneously exposed to a first reactant and a secondreactant, and subjected to modulated ion 177 exposure. By modulating 1)the ion flux (i.e. the number of ions hitting the substrate per unitarea per unit time); 2) the energy of the ions striking the substrate;or a combination of (1) and (2), the deposition reaction can beprecisely toggled “on” or “off”. Since the substrate 181 is preferablymaintained at a low substrate temperature, the first and secondreactants do not thermally react with any appreciable rate or do notreact at all when the ion flux or energy is toggled to a “low” state.Instead, the deposition reaction only takes place when either the ionflux or ion energy is toggled to a suitable “high state”. Ion flux orenergy modulation can vary generally from 0.1 Hz to 20 MHz, preferablyfrom 0.01 KHz to 10 KHz. During deposition, the main process chamber 180pressure can be maintained in the range of generally 10² to 10⁷ torr,more preferably from 10¹ to 10⁴ torr, depending on the chemistryinvolved. The desired film thickness is attained via exposure of thesubstrate to the suitable number of modulated ion flux or energy pulsecycles. This MII-ALD scheme results in a “continuous” deposition processthat is significantly faster than conventional sequential ALD since thetwo, slow evacuation steps (up to minutes) are eliminated and replacedby the faster (KHz range or above) ion modulation steps. The modulationcan be either of the ion flux via the plasma power or of the ion energyvia an applied periodic wafer bias.

The MII-ALD method utilizing ion flux modulation to control thedeposition cycle is illustrated conceptually in FIG. 3A, with the fluxmodulation scheme described more explicitly in FIGS. 4A and 4C. FIG. 3Adepicts the MII-ALD method utilizing ion flux modulation 320 to vary thesubstrate 181 exposure to ions 177. Note that the second reactant 310,e.g., radicals, is synchronized with the ion flux via 320 plasma powermodulation, causing a periodic exposure of the substrate to ions andradicals. Varying the power 160 delivered to the plasma 172 can vary theion flux from little or none to maximum ion production. Plasma powermodulation can take the form of variations in frequency (periodicity),magnitude, and duty-cycle. Increasing plasma power 160 leads toincreasing plasma 172, and hence, increased ion 177 density. Since thedeposition process is ion-induced, having little or no ion bombardmentwill essentially stop the deposition process, whereas increased ionbombardment will cause deposition to occur. A constant wafer bias 185(DC in FIG. 4C or RF in FIG. 4A) is applied to define the ion energy ofthe modulated ion flux in this embodiment and is chosen to besufficiently high so that ion-induced surface reactions can occur. Notethat in this embodiment since the plasma (either RF or preferablymicrowave) power 160 is used to generate both ions 177 and radicals 176,the second reactant (e.g., radicals) flux 310 is synchronized with theion flux 320 pulses. The radical feed gas 110 (H₂ for example) flow,however, does riot change. Instead, the radical flux 310 (e.g., fractionof H₂ which is converted to atomic H) is modulated.

Alternatively, subjecting the substrate 181 to a non-constant wafervoltage bias 185 can vary the incoming ion energy at a fixed plasmapower 160 (i.e., ion flux). This preferred embodiment of MII-ALD isillustrated conceptually in FIG. 3B, and more explicitly in FIGS. 4B and4D. FIG. 3B shows the MII-ALD method utilizing ion energy modulation 350to vary the substrate 181 exposure to ions 177 by varying the substratebias 185. The applied bias 185 can take the form of variations infrequency (periodicity), magnitude, and duty-cycle. A DC as shown inFIG. 4D or RF (e.g., 400 kHz, 2 MHz, 13.56 MHz, etc.) as shown in FIG.4B power supply can be used. When the wafer potential is “low” (e.g.,near or at zero with respect to ground), the incoming ions 177 do nothave enough energy to induce surface deposition reactions. When thewafer 181 potential is “high” (e.g., at a significant negative potentialrelative to ground), the incoming ions 177 will have the necessaryenergy to induce surface deposition reactions via collision cascades. Insuch a fashion, the deposition can be turned “on” or “off” by modulatingthe wafer bias voltage 185, and hence the impinging ion 177 energy.Typical wafer voltages can range from generally −20 V to −1000 V, butpreferably in the −25 V to −500 V range, and more preferably in the −50V to −350 V range during deposition. The bias voltage 185 is coupled tothe wafer via the pedestal 182. Preferably, the substrate pedestal 182is an electrostatic chuck (ESC) to provide efficient coupling of biasvoltage to the substrate. The ESC is situated in the main processingchamber 180 and can be cooled via a fluid coolant (preferably a liquidcoolant) and/or heated (e.g., resistively) to manipulate the substratetemperature.

As illustrated in FIG. 5 for the case of an applied DC bias, thepreferred electrostatic chuck is a “coulombic” ESC 500 (bulk resistivitygenerally greater than 10¹³ ohm-cm) rather than one whose bulk materialeffects are dominated by the Johnson-Rahbek (JR) effect (bulkresistivity between 10⁸ and 10¹² ohm-cm). Typically, the substratepotential is a complex function of the voltage of the electrostatic“chucking” electrodes if these voltages are established relative to areference potential, but is simplified in the case of “coulombic”(non-JR) ESC. However, if the power supply 510 that powers the ESC 500is truly floating, i.e., the entire system has a high impedance to thechamber 180 potential (usually ground) including the means of supplyingpower, then the substrate potential can be arbitrary. In particular, ifthe ESC power supply 510 is also center-tapped 518, then the waferpotential can be established by connecting the center tap 518 to theoutput of a power amplifier 520. A waveform generator 535 coupled to thepower amplifier 520 can be controlled by a control computer 195 (FIGS. 1and 6) to, for example, periodically drop the substrate potential to anegative value for a certain period of time or apply a given frequencyto the ESC 500. It is desired to have independent control of themagnitude, frequency (periodicity), and duty cycle of this substratebias pulse train. Such an ESC system is depicted in FIG. 5, which showsan ESC system suitable for modulating the ion energy in the MII-ALDprocess: a) in topological form; and, b) as an equivalent electricalcircuit.

The deposition rate is affected by the choice of the critical bias pulsetrain variables: the magnitude, frequency (periodicity), and duty cycle.Preferably, when the bias frequency is high (e.g., 100 Hz-10 KHz) with ashort duty cycle (e.g., less than 30%), reducing the net, time-averagedcurrent (which can cause substrate potential drift, de-chuckingproblems, or charge-induced device damage) while providing a chargerelaxation period wherein the ion charges accumulated during ionexposure can redistribute and neutralize.

Once the deposition rate is calibrated for a particular recipe(Angstroms/cycle), the ability to accurately determine the filmthickness by counting cycles is a further benefit of this modulationscheme. The higher the frequency, the finer the resolution of thiscritical deposition process performance metric.

Alternatively, the substrate potential can be modulated by imparting aninduced DC bias to the substrate by applying RF power to the pedestal.Preferably, the RF power is coupled into the ESC electrodes. FIGS. 4A-Fillustrate the preferred methods of modulating the MII-ALD process. InFIG. 4A, an RF bias power B₂ is applied to the substrate pedestal 182imparting an induced DC bias V₂ to the substrate while the plasma(either microwave or RF) power 400 is varied periodically between a highP₁ and a low P₂ power state. In FIG. 4B, plasma (either microwave or RF)power 410 is constant P₁ while an RF bias power, applied to thesubstrate pedestal 182, is varied between a low B₁ and a high B₂ biasstate (V₁ and V₂ are the DC offset or bias voltages resulting from theapplied RF bias power). In FIG. 4C, a negative DC bias 425 is applied tothe substrate pedestal 182 while the plasma (either microwave or RF)power 420 is varied periodically between a high P₁ and a low power P₂state. In FIG. 4D, plasma (either microwave or RF) power is constant 430while a DC bias 435 applied to the substrate pedestal 182 is variedbetween a zero V₁ and a negative voltage state V₂. In FIG. 4E, amechanical shutter periodically occludes the ion source. All the while,the plasma power 440 (either microwave or RF) and substrate voltage 445are held constant. In FIG. 4F, a source area that is smaller than thesubstrate 181 is preferably used. In this case, plasma (either microwaveor RF) power 450 is constant, a negative DC substrate bias 455 isconstant, and the source and substrate 181 are moved relative to eachother 457, exposing only a portion of the substrate 181 at a time. Themethods proposed in FIG. 4B and FIG. 4D, whereby the substrate bias ismodulated at a constant plasma power 410, 430 and hence ion flux, aremost preferred.

MII-ALD can be used to deposit dielectric, semiconducting, or metalfilms, among others, used in the semiconductor, data storage, flat paneldisplay, and allied as well as other industries. In particular, themethod and apparatus is suitable for the deposition of barrier layers,adhesion layers, seed layers, low dielectric constant (low-k) films, andhigh dielectric constant (high-k) films.

This process utilizes independent control over the three constituents ofplasma—ions, atoms, and precursors. Decoupling these constituents offerimproved control over the deposition process.

An added benefit of using MII-ALD is that with proper choice of thesecond reactant, selective ion-enhanced etching and removal of unwantedimpurities can be performed. As an example, for many chemistries, thepreferred second reactant is monatomic hydrogen (H) 176. Simultaneousenergetic ion and reactive atomic H bombardment will cause selectiveremoval of unwanted impurities (e.g., containing carbon, oxygen,fluorine, or chlorine) commonly associated with organometallicprecursors (e.g., TBTDET, PEMAT, PDEAT, TDMAT, TDEAT), and proceed withremoval rates superior to either chemical reaction (e.g., atomic H only)or physical sputtering (e.g., Ar ion only) alone. Impurities lead tohigh film resistivities, low film density, poor adhesion, and otherdeleterious film effects. Alternatively, in addition to atomic hydrogen,other reactive groups such as nitrogen atoms (N), oxygen atoms (O), OHmolecules, or NH molecules, or a combination thereof may be employed.

FIG. 6 illustrates another embodiment of a deposition system suitablefor modulated ion-induced atomic layer deposition (MII-ALD). In theembodiment shown in FIG. 6 all of the ion/radical generating feed gasesand the precursor gases are introduced into the chamber via adistribution showerhead 171 or via another means of uniformlydistributing gases essentially parallel or perpendicular to a face of asubstrate 181, which are well-known to one skilled in the art. It willbe appreciated that although the showerhead 171 is shown to be above thesubstrate 181 to direct a gas flow downwards towards the substrate 181,alternative lateral gas introduction schemes are possible with thisembodiment and with the previously described embodiments. In one suchexemplary alternative shown in FIG. 8, a cross-flow arrangementintroduces gas 801 from at least one side of a main processing chamber803 via one or more apertures whose axes are largely parallel. Inanother exemplary alternative shown in FIG. 7, one or more radialapertures spaced about the periphery of a main processing chamber 703configured to introduce a gas 701 can also be used. One skilled in theart may also readily conceive of alternative arrangements, such as theexemplary arrangement shown in FIG. 9. FIG. 9 utilizes both a flow ofgas perpendicular 905 and radially parallel 901 to a face of substrate181.

In the embodiment shown in FIG. 6, a source of RF bias power 160 iscoupled to one or more ESC electrodes 603 in the substrate pedestal 182.The ESC electrodes 603 may be of any arbitrary shape. The RF bias powerprovides power for both ion generation during modulated ion inducedatomic layer deposition and energy control of the generated ions. Theapplied RF bias power is used to generate a plasma, for example, betweenthe substrate 181 and the showerhead 171 to dissociate feed gases togenerate ions and/or radicals and to induce a negative potentialV_(bias) 185 (i.e., a DC offset voltage typically −10 V to −80 V at ≦150W RF power and 0.1-1 Torr pressure) on the substrate 181. The negativepotential V_(bias) 185 modulates the energy of the positively chargedions in the plasma and attracts the positively charged ions toward thesurface of substrate. The positively charged ions impinge on thesubstrate 181, driving the deposition reaction and improving the densityof the deposited film. The ion energy is more specifically given byE=e|V_(p)|+e|V_(bias)|, where V_(p) is the plasma potential (typically10 V to 20 V) and V_(bias) is the negative potential V_(bias) 185induced on the substrate 181. The negative potential V_(bias) 185 iscontrolled by the applied RF bias power. For a given process regiongeometry, the induced negative potential V_(bias) 185 increases withincreasing RF bias power and decreases with decreasing RF bias power.

Controlling the RF bias power also controls the density and hence thenumber of ions generated in the plasma. Increasing the RF bias powergenerally increases the ion density, leading to an increase in the fluxof ions impinging on the substrate. Higher RF bias powers are alsorequired for larger substrate diameters. A preferred power density is≦0.5 W/cm², which equates to approximately ≦150 W for a 200 mm substrate181. Power densities ≧3 W/cm² (greater than about 1000 W for a 200 mmdiameter substrate 181) may lead to undesired sputtering of thedeposited film.

The frequency of the RF bias power can be 400 kHz, 13.56 MHz, or higher(e.g. 60 MHz, etc.). The low frequency (e.g. 400 kHz), however, can leadto a broad ion energy distribution with high energy tails which maycause excessive sputtering. The higher frequencies (e.g., 13.56 MHz orgreater) lead to tighter ion energy distributions with lower mean ionenergies, which is favorable for modulated ion-induced ALD depositionprocesses. The more uniform ion energy distribution occurs because theRF bias polarity switches before ions can impinge on the substrate, suchthat the ions see a time-averaged potential.

As shown in FIG. 6, a source of applied DC bias can also be coupled tothe ESC substrate pedestal 182. The source can be a DC power supply 510coupled by a center tap 518 to a voltage source 525 with the ability tovary the voltage or exhibit an infinite impedance. Optionally, avariable impedance device 605 may be coupled in series between thevoltage source 525 and the center tap 518 of the DC power supply 510.The voltage source 525 is itself coupled to a waveform generator 535.The waveform generator 535 may be a variable-type waveform generator. Anexemplary variable-type waveform generator may be controlled by acontrol computer 195 and have a variable waveform at different timeswithin a given process and may additionally have a non-periodic outputsignal. The source of applied DC bias can be coupled to the ESCsubstrate pedestal 182 by RF blocking capacitors 601 that both provide aDC open for the DC power supply 510 and prevent RF energy fromcorrupting the DC power supply 510.

From the description of the preferred embodiments of the process andapparatus set forth above, it is apparent to one of ordinary skill inthe art that variations and additions to the embodiments can be madewithout departing from the principles of the present invention. As anexample, chlorine, bromine, fluorine, oxygen, nitrogen, hydrogen, otherreactants and/or radicals containing the aforementioned elements or acombination thereof, in conjunction with energetic ion bombardment, canbe used to effect etching or material removal as opposed to deposition.This is of particular importance in the cleaning of native oxides ofcopper, aluminum, silicon, and other common conductor and semiconductormaterials used in IC manufacturing. Either the deposition or etching canbe accomplished globally (as illustrated in the preceding embodiments)or may be chosen to be local to a controlled area (i.e., site-specificusing a small, ion beam point or broad-beam source scanned or otherwisestepped across the substrate, exposing only a fraction of the substratearea at any given time).

1-6. (canceled)
 7. A sequential method for depositing a thin film onto asubstrate in a chamber comprising: introducing a first reactant gasselected from the group consisting of copper (I) β-diketonates, copper(II) β-diketonates, and copper halides into said chamber; adsorption ofat least one monolayer of said first reactant gas onto said substrate;removing excess said first reactant gas from said chamber; introducingat least one ion generating feed gas into said chamber; introducing atleast one radical generating feed gas into said chamber; generating aplasma from said ion generating feed gas and said radical generatingfeed gas to form ions and radicals; exposing said substrate to said ionsand said radicals; modulating said ions; and reacting said adsorbedmonolayer of said first reactant gas with said ions and said radicals todeposit said thin film.
 8. The method of claim 7 wherein said firstreactant gas is selected from the group comprising Cu(thd)₂, Cu(acac)₂,and Cu(hfac)₂.
 9. A modulated ion-induced atomic layer depositionsystem, comprising: a deposition chamber; a means of introducing gasesinto said deposition chamber; a substrate holder located within saiddeposition chamber, said substrate holder having a DC power supply tosupply a DC voltage to at least one electrode contained in saidsubstrate holder; a source of RF bias power electrically coupled to bothan output of said DC power supply and to said at least one electrode; avoltage source electrically coupled to said DC power supply by couplingan output of said voltage source to a center tap of said DC powersupply; a variable waveform generator coupled to an input of saidvoltage source; and a plurality of blocking capacitors electricallycoupled to said output of said DC power supply and said source of RFbias power, said plurality of blocking capacitors configured in a way soas to allow said DC voltage to be coupled to said at least one electrodeand prevent an RF energy produced by said source of RF bias power fromcorrupting said DC power supply.